Light fittings which require watertightness, such as outside lights, diving lights and so on, must be equipped with a gasket at the joint of the light shade and the light frame (or lens frame) to achieve watertightness. The gasket, which is usually made from elastic material like silica gel or latex is maintained at the joint of the light shade and the light frame. When the light shade and the light frame are locked together, the elastic and gasket will fill in the gap at the joint so as to form a hermetic seal and ensure watertightness.
The general method of retaining a gasket at the joint is to make a groove in the light shade for inserting the gasket. The gasket has a greater height than the depth of the groove, so as to protrude a little bit over the groove to ensure the gasket fills in the gap at the joint when the light shade is locked tightly to the light frame, making the light fitting watertight.
The groove for retaining the gasket is usually made directly on the light shade. There are two specific methods for making the groove. FIGS. 1 and 2 illustrate the two different methods of the prior art. As shown in FIG. 1, one method for making the groove is to make an outstretched step (or annular flange) 2 around the outer edge of the light shade to form groove 3 for inserting the gasket at the joint between the edge side of the flange and the shade wall. This method is particularly useful when the wall of light shade is somewhat thin. This kind of light fitting is not aesthetically pleasing because of the outstretched step 2. As shown in FIG. 2, a second method for making the groove is to make the wall of shade 4 thicker and make a gasket groove 5 directly on the wall of shade 4. This kind of light fitting has even and smooth outside surfaces but is heavy and impractical for easy use. It is also costly because of the thicker shade wall which utilizes excessive material. Furthermore, the amount of defective product obtained during manufacture is high. Therefore, it is desirable to provide an aesthetically pleasing watertight light with a thin wall that it is cost effective.